Note 8 - Segment Information - Results of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2019	May 31, 2018	May 31, 2019	May 31, 2018	Aug. 31, 2018
Revenue from clients	$ 364,533	$ 339,911	$ 1,071,068	$ 1,004,283
Segment operating income	117,240	93,265	326,467	277,848
Total assets	1,511,901	1,407,172	1,511,901	1,407,172	$ 1,419,447
Capital expenditures	11,424	6,000	32,906	18,375
UNITED STATES
Revenue from clients	226,961	210,308	672,479	627,976
Segment operating income	51,012	37,986	140,549	117,285
Total assets	820,078	728,517	820,078	728,517
Capital expenditures	8,664	2,830	20,022	10,104
Europe [Member]
Revenue from clients	102,499	98,856	299,197	286,789
Segment operating income	44,793	37,381	127,130	107,344
Total assets	569,609	572,867	569,609	572,867
Capital expenditures	439	537	2,136	2,816
Asia Pacific [Member]
Revenue from clients	35,073	30,747	99,392	89,518
Segment operating income	21,435	17,898	58,788	53,219
Total assets	122,214	105,788	122,214	105,788
Capital expenditures	$ 2,321	$ 2,633	$ 10,748	$ 5,455